From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755331AbbAWOiT (ORCPT ); Fri, 23 Jan 2015 09:38:19 -0500 Received: from mail-pd0-f172.google.com ([209.85.192.172]:57698 "EHLO mail-pd0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750900AbbAWOiP (ORCPT ); Fri, 23 Jan 2015 09:38:15 -0500 Date: Fri, 23 Jan 2015 23:38:49 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nitin Gupta , Jerome Marchand , Sergey Senozhatsky Subject: Re: [PATCH 2/2] zram: protect zram->stat race with init_lock Message-ID: <20150123143849.GB2320@swordfish> References: <1421992707-32658-1-git-send-email-minchan@kernel.org> <1421992707-32658-2-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1421992707-32658-2-git-send-email-minchan@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (01/23/15 14:58), Minchan Kim wrote: > The zram->stat handling should be procted by init_lock. > Otherwise, user could see stale value from the stat. > > Signed-off-by: Minchan Kim > --- > > I don't think it's stable material. The race is rare in real practice > and this stale stat value read is not a critical. > > drivers/block/zram/zram_drv.c | 37 ++++++++++++++++++++++++++++--------- > 1 file changed, 28 insertions(+), 9 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 0299d82275e7..53f176f590b0 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -48,8 +48,13 @@ static ssize_t name##_show(struct device *d, \ > struct device_attribute *attr, char *b) \ > { \ a side note: I wasn't Cc'd in that patchset and found out it only when it's been merged. I'm not sure I understand, why it has been renamed from specific zram_X_show to X_show. what gives? can't help, catches my eye every time, that rename has broken the original formatting: diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9250b3f..c567af5 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -44,7 +44,7 @@ static const char *default_compressor = "lzo"; static unsigned int num_devices = 1; #define ZRAM_ATTR_RO(name) \ -static ssize_t name##_show(struct device *d, \ +static ssize_t name##_show(struct device *d, \ struct device_attribute *attr, char *b) \ { \ struct zram *zram = dev_to_zram(d); \ I don't have any objections. but do we really want to wrap atomic ops in semaphore? it is really such serious race? -ss > struct zram *zram = dev_to_zram(d); \ > - return scnprintf(b, PAGE_SIZE, "%llu\n", \ > - (u64)atomic64_read(&zram->stats.name)); \ > + u64 val = 0; \ > + \ > + down_read(&zram->init_lock); \ > + if (init_done(zram)) \ > + val = atomic64_read(&zram->stats.name); \ > + up_read(&zram->init_lock); \ > + return scnprintf(b, PAGE_SIZE, "%llu\n", val); \ > } \ > static DEVICE_ATTR_RO(name); > > @@ -67,8 +72,14 @@ static ssize_t disksize_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > struct zram *zram = dev_to_zram(dev); > + u64 val = 0; > + > + down_read(&zram->init_lock); > + if (init_done(zram)) > + val = zram->disksize; > + up_read(&zram->init_lock); > > - return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize); > + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > } > > static ssize_t initstate_show(struct device *dev, > @@ -88,9 +99,14 @@ static ssize_t orig_data_size_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > struct zram *zram = dev_to_zram(dev); > + u64 val = 0; > + > + down_read(&zram->init_lock); > + if (init_done(zram)) > + val = atomic64_read(&zram->stats.pages_stored) << PAGE_SHIFT; > + up_read(&zram->init_lock); > > - return scnprintf(buf, PAGE_SIZE, "%llu\n", > - (u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT); > + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > } > > static ssize_t mem_used_total_show(struct device *dev, > @@ -957,10 +973,6 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > struct bio_vec bv; > > zram = bdev->bd_disk->private_data; > - if (!valid_io_request(zram, sector, PAGE_SIZE)) { > - atomic64_inc(&zram->stats.invalid_io); > - return -EINVAL; > - } > > down_read(&zram->init_lock); > if (unlikely(!init_done(zram))) { > @@ -968,6 +980,13 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > goto out_unlock; > } > > + if (!valid_io_request(zram, sector, PAGE_SIZE)) { > + atomic64_inc(&zram->stats.invalid_io); > + err = -EINVAL; > + goto out_unlock; > + } > + > + > index = sector >> SECTORS_PER_PAGE_SHIFT; > offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; > > -- > 1.9.1 > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id D00AB6B0032 for ; Fri, 23 Jan 2015 09:38:15 -0500 (EST) Received: by mail-pd0-f175.google.com with SMTP id fl12so8872026pdb.6 for ; Fri, 23 Jan 2015 06:38:15 -0800 (PST) Received: from mail-pd0-x22a.google.com (mail-pd0-x22a.google.com. [2607:f8b0:400e:c02::22a]) by mx.google.com with ESMTPS id su9si2083630pab.162.2015.01.23.06.38.14 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 23 Jan 2015 06:38:14 -0800 (PST) Received: by mail-pd0-f170.google.com with SMTP id p10so8913153pdj.1 for ; Fri, 23 Jan 2015 06:38:14 -0800 (PST) Date: Fri, 23 Jan 2015 23:38:49 +0900 From: Sergey Senozhatsky Subject: Re: [PATCH 2/2] zram: protect zram->stat race with init_lock Message-ID: <20150123143849.GB2320@swordfish> References: <1421992707-32658-1-git-send-email-minchan@kernel.org> <1421992707-32658-2-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1421992707-32658-2-git-send-email-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nitin Gupta , Jerome Marchand , Sergey Senozhatsky On (01/23/15 14:58), Minchan Kim wrote: > The zram->stat handling should be procted by init_lock. > Otherwise, user could see stale value from the stat. > > Signed-off-by: Minchan Kim > --- > > I don't think it's stable material. The race is rare in real practice > and this stale stat value read is not a critical. > > drivers/block/zram/zram_drv.c | 37 ++++++++++++++++++++++++++++--------- > 1 file changed, 28 insertions(+), 9 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 0299d82275e7..53f176f590b0 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -48,8 +48,13 @@ static ssize_t name##_show(struct device *d, \ > struct device_attribute *attr, char *b) \ > { \ a side note: I wasn't Cc'd in that patchset and found out it only when it's been merged. I'm not sure I understand, why it has been renamed from specific zram_X_show to X_show. what gives? can't help, catches my eye every time, that rename has broken the original formatting: diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9250b3f..c567af5 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -44,7 +44,7 @@ static const char *default_compressor = "lzo"; static unsigned int num_devices = 1; #define ZRAM_ATTR_RO(name) \ -static ssize_t name##_show(struct device *d, \ +static ssize_t name##_show(struct device *d, \ struct device_attribute *attr, char *b) \ { \ struct zram *zram = dev_to_zram(d); \ I don't have any objections. but do we really want to wrap atomic ops in semaphore? it is really such serious race? -ss > struct zram *zram = dev_to_zram(d); \ > - return scnprintf(b, PAGE_SIZE, "%llu\n", \ > - (u64)atomic64_read(&zram->stats.name)); \ > + u64 val = 0; \ > + \ > + down_read(&zram->init_lock); \ > + if (init_done(zram)) \ > + val = atomic64_read(&zram->stats.name); \ > + up_read(&zram->init_lock); \ > + return scnprintf(b, PAGE_SIZE, "%llu\n", val); \ > } \ > static DEVICE_ATTR_RO(name); > > @@ -67,8 +72,14 @@ static ssize_t disksize_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > struct zram *zram = dev_to_zram(dev); > + u64 val = 0; > + > + down_read(&zram->init_lock); > + if (init_done(zram)) > + val = zram->disksize; > + up_read(&zram->init_lock); > > - return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize); > + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > } > > static ssize_t initstate_show(struct device *dev, > @@ -88,9 +99,14 @@ static ssize_t orig_data_size_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > struct zram *zram = dev_to_zram(dev); > + u64 val = 0; > + > + down_read(&zram->init_lock); > + if (init_done(zram)) > + val = atomic64_read(&zram->stats.pages_stored) << PAGE_SHIFT; > + up_read(&zram->init_lock); > > - return scnprintf(buf, PAGE_SIZE, "%llu\n", > - (u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT); > + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > } > > static ssize_t mem_used_total_show(struct device *dev, > @@ -957,10 +973,6 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > struct bio_vec bv; > > zram = bdev->bd_disk->private_data; > - if (!valid_io_request(zram, sector, PAGE_SIZE)) { > - atomic64_inc(&zram->stats.invalid_io); > - return -EINVAL; > - } > > down_read(&zram->init_lock); > if (unlikely(!init_done(zram))) { > @@ -968,6 +980,13 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > goto out_unlock; > } > > + if (!valid_io_request(zram, sector, PAGE_SIZE)) { > + atomic64_inc(&zram->stats.invalid_io); > + err = -EINVAL; > + goto out_unlock; > + } > + > + > index = sector >> SECTORS_PER_PAGE_SHIFT; > offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; > > -- > 1.9.1 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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